1. Field of the Invention
The present invention relates to optical communication, and more specifically, it relates to a beam splitter designed such that the phase difference between the two interference beams is independent of the polarization status of the incident beam.
2. Description of Related Art
An un-polarized beam splitter (UBS) is popularly used in interferometers such as the Michelson (FIG. 1) and the Mach-Zehnder (FIG. 2). In the conventional Michelson interferometer of FIG. 1, the incident light 10 from the left-hand side of beam-splitter 12 is separated into two beams; part of the power is reflected (14) from the beam splitter and the rest of light is transmitted (16). After those two beams (16,14) are reflected from mirrors M1 and M2 respectively, beam 16 is reflected by, and beam 14 is transmitted through, beam-splitter 12 again. The interference takes place at both the bottom 18 and the left 20 of the beam-splitter. Constructive interference takes place when the optical path length difference (OPD) is an integer multiplication of wavelength. Since the total energy is conserved, the summation of optical power at the bottom arm and the left arm should be equal to the optical power delivered from the light source. In other words, when constructive interference occurs at the bottom arm, destructive interference occurs at the left arm.
It would be advantageous if a beam splitter for use in an interferometer were available such that the phase difference between the two interference beams were polarization independent